In this recent answer, user Aubrey speaks about the use of images from Wikimedia in posters.
I think that she should disclose the fact that she is president of the Italian branch of Wikimedia; this bit of information currently appears on her profile, but not in the answer itself.
In the comments, she seems to disagree with my view, so I think I should ask for further opinions from users and moderators.
I don't think there is any significant problem with the answer as it stands. Here is why I differentiate it from the "advertising" posts that have been problematic in the past:
Most advertising posts introduce the subject that they are advertising (e.g., "problems with students cheating on exams? why not use Cheat-Be-Gone, now with lemon scent!"). Here the OP introduced the subject, and simply drew an answer written by an expert.
I found the post mostly simply adding clarification and information, rather than advocating Wikimedia vs. other sources. This is a post that could easily have been written by anybody familiar with the resource---in fact, much of it are things that I would consider nearly "common knowledge."
That said, disclosure never hurts, and in this case would probably be nice simply in adding to the authority of the answer. For example, when I write an answer to a post about how journals work, I will often mention the service I have done as an editor simply as part of credentialing my answer. I thus think that this answer could be enhanced by disclosure, less for ethical reasons and more to make clear the expertise of the author.
I would like to make some clarifications.
Of course, and that is probably the thing we want to discuss, I am biased towards open access and open knowledge. I'm an advocate (someone would consider me an activist), and I understand my answer is not neutral, because I'm not. I alsways try to ground my answers and comments with reason and facts, but I do have a strong opinion regarding certain topics. I cannot help it :-)
I don't think there's a huge conflict of interest here, as the user in question is not in a position to profit directly or indirectly from increased Wikimedia Commons usage.
That said, it certainly doesn't hurt to provide that information upfront when one is talking about something that could appear to be a conflict. However, I would be careful about making more requirements. I think the existing rules are sufficient.
As an addendum to other answers, my perspective is that once the conflict of interest is fuzzy enough, there is a benefit to leaving it out: people don't care too much, and would rather spend their time reading something else. As an analogy, academic talks also often omit details in proofs to maximize the information/time tradeoff. Those details are relevant, but not worth people's time.
My opinion is that full disclosure of this potential conflict of interest is necessary in the answer itself.
The question is "would use of Wikimedia images be considered unprofessional"; it is a subjective question, and it is clear that being president of a national Wikimedia branch affects significantly her view on this topic. The fact that she is not paid for this position is irrelevant.
Disclosure of this fact in her profile is not sufficient: first of all it is information that should not be one click away from the answer, and more importantly profiles (unlike answers) can be changed at any time without notice.
Her answer is (unnecessarily) apologetic of Wikimedia images in several passages:
it is possible to find great images in Commons
There are great pictures on Commons.
There are many professionals who use their free time to provide Commons (and hence Wikipedia articles) with illustrative, clear graphics.
It should be made clear that this is not the opinion of an independent academic user, but the one of a person who is significantly involved in the project.
I have nothing against her, Wikimedia or her answer, and I welcome her contributions to this site, but I think that an user should disclose this kind of information whenever they reference explicitly an organization in which they are actively involved. We have had some cases of advertising of one's own projects on this site, and it is always better to err on the side of transparency.
(full disclosure: I have contributed to Wikipedia by editing a few pages in the past.) :)
